Soil Springs for Buried Pipeline Axial Motion

The response of a buried pipeline to seismic waves is controlled by differential movements along its length. The axial movement of the pipeline is restrained by friction forces at the soil-pipe interface. Tests performed by others on a full scale pipe indicate that the relationship between the soil resistant force and relative displacement (i.e., between the soil and the pipe) is linear at small displacements. This soil resistant force reaches a ``plateau'' when shippage of the pipe with respect to the soil occurs. This suggests that the axial soil-pipe interaction can be modeled by discrete spring-sliders distributed along the pipeline. The initial stiffness of these spring-sliders is the subject of this technical note. First, previous studies evaluating this initial soil axial stiffness are reviewed. Then, results from the field tests are used to backcalculate the value of the initial soil stiffness. On the basis of the results obtained, a range of values is proposed to estimate the initial soil axial stiffness.